The configuration of a container end closure affects the level to which end consumers, as well as bottlers, manufacturers, distributors, shippers, and retailers, are satisfied with a beverage container. One factor is the opening characteristics of the container, including the ease and reliability of opening the container. Many beverage containers currently are provided with easy-open end closures, commonly referred to as “stay-on-tab” or “SOT” end closures, in which a pull tab is interconnected to a central panel by a rivet. In these container end closures, the central panel includes a tear panel defined by a curvilinear score line and a hinge line formed between the end points of the score line. Generally, pulling upward on a lift end of the tab pivots the tab about the rivet and presses the nose of the tab downward on the tear panel. Sufficient downward force exerted on the tear panel by the nose of the tab causes the score line to fracture, thus permitting the tear panel to bend or pivot inward about the hinge line. The downward displacement of the tear panel creates an opening for dispensing the contents of the container. Both the tear panel and the pull tab remain attached to the end closure after opening, thus reducing pollution and the possibility of a user ingesting the tab.
To facilitate the opening of the tear panel, some stay-on-tab end closures currently utilize features formed in the tear panel to stiffen the tear panel and/or gather slack metal created during formation of the score line. For example, some existing stay-on-tab end closures include a raised u-shaped bead projecting upward from the public side of the tear panel or a recessed u-shaped bead projecting downward from the product side of the tear panel. When these end closures are seamed and sealed to a container filled with a carbonated beverage, the tear panels tend to exhibit doming despite the presence of the bead. Examples of these conventional stay-on-tab end closures are provided in U.S. Patent Publication No. 2007/0108208 and U.S. Pat. Nos. 5,219,257; 6,161,717; 6,405,889; 7,000,797; and 7,165,696, the entire disclosures of which are hereby incorporated herein by reference.
Further, some existing stay-on-tab end closures include a tear panel having a depressed region. The depressed region does not sufficiently stiffen the tear panel and does not adequately remove slack metal displaced during score formation. An example of this type of stay-on-tab end closure is provided in U.S. Pat. No. 5,875,911, the entire disclosure of which is hereby incorporated herein by reference.
Thus, there is a need to provide a container end closure that provides enhanced opening characteristics over existing stay-on-tab end closures. For example, there is a need in the industry for a stay-on-tab end closure that has a stiffened tear panel. In addition, there is a need for a stay-on-tab end closure with reduced doming of the tear panel when the container is subject to increased internal pressure, such as when the container is filled with a carbonated beverage. Doming of the end panel, and especially doming of the tear panel, results in increased fracture resistance of the tear panel, which reduces the effectiveness of the stay-on-tab end closure and increases the likelihood of premature fracturing and leakage during storage or transportation.